1. Field of the Invention
The present invention relates to semiconductor pressure detecting devices. More specifically, the present invention relates to semiconductor pressure detecting devices using the piezoresistance effect.
2. Description of Prior Art
FIG. 8 shows a schematic lateral cross section of a conventional semiconductor pressure detecting device, including a silicon chip 1 for converting measured pressure into a voltage and mounted on a pedestal, for example, a silicon pedestal 5. The silicon pedestal 5 is arranged to relieve external stress imposed on the silicon chip 1. The silicon pedestal 5, on which the silicon chip has previously been die-bonded, is mounted on a stem 6 by die bonding. Arranged on this stem 6 is a pressure introduction pipe 7 for transmitting external pressure to the silicon chip 1. The silicon chip 1 is electrically connected with an external apparatus via wires 8 wire-bonded to the silicon chip 1, and leads 9 supported in the stem 6 with an insulating material 12. The silicon chip 1, wire 8, and other elements are covered with a metallic cap 11 having a relief opening 10.
In the conventional semiconductor pressure sensor, pressure introduced through the pressure introduction pipe 7 is applied to the silicon chip 1, converted into voltage by the silicon chip 1, and then output via the wire 8 and lead 9.
FIG. 9 is a plan view showing the silicon chip 1 of the semiconductor pressure detecting device illustrated in FIG. 8, while FIG. 10 is a side view of the silicon chip 1. In these figures, the silicon chip 1 has a (100) crystalline surface. On the reverse side of the silicon chip 1, a thin portion 2 is formed, and gauge resistances 3a to 3d are located on four corners of the surface of the silicon chip 1 corresponding to the thin portion 2.
The conventional semiconductor pressure detecting device and its gauge resistances are formed as illustrated in FIG. 7. Namely, by means of conventional laser recrystallization, a recrystallized silicon film 15 was produced in the (100) direction from seeds 13 and 14 by heating with a laser. However, a subgrain boundary 16, a crystalline fault, occurs at the boundary of the recrystallized silicon film 15. Conventionally, p-type gauge resistances 3 have been employed to avoid this subgrain boundary 16.
In the semiconductor pressure detecting device described above, even if a gauge resistance is arranged in order to avoid a subgrain boundary, some subgrain boundaries are produced, resulting in non-uniform resistances of the gauge resistors, and also greatly non-uniform offset voltages. Further, the temperature coefficient of resistance is non-linear. Because of these problems, it is very difficult to compensate for the temperature characteristics of the semiconductor pressure detecting device and a high-precision semiconductor pressure detecting device cannot be provided.